target: Add missing mapped_lun bounds checking during make_mappedlun setup

This patch adds missing bounds checking for the configfs provided
mapped_lun value during target_fabric_make_mappedlun() setup ahead
of se_lun_acl initialization.

This addresses a potential OOPs when using a mapped_lun value that
exceeds the hardcoded TRANSPORT_MAX_LUNS_PER_TPG-1 value within
se_node_acl->device_list[].

Reported-by: Jan Engelhardt <jengelh@inai.de>
Cc: Jan Engelhardt <jengelh@inai.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>